Coronary artery disease (CAD) is the major cause of death in Type 2 diabetic and metabolic syndrome patients (i.e. patients that fall within the ‘deadly quartet’ category of impaired glucose tolerance, insulin resistance, hypertriglyceridaemia and/or obesity).
The hypolipidaemic fibrates and antidiabetic thiazolidinediones separately display moderately effective triglyceride-lowering activities although they are neither potent nor efficacious enough to be a single therapy of choice for the dyslipidaemia often observed in Type 2 diabetic or metabolic syndrome patients. The thiazolidinediones also potently lower circulating glucose levels of Type 2 diabetic animal models and humans. However, the fibrate class of compounds are without beneficial effects on glycaemia. Studies on the molecular actions of these compounds indicate that thiazolidinediones and fibrates exert their action by activating distinct transcription factors of the peroxisome proliferator activated receptor (PPAR) family, resulting in increased and decreased expression of specific enzymes and apolipoproteins respectively, both key-players in regulation of plasma triglyceride content.
PPARδ activation was initially reported not to be involved in modulation of glucose or triglyceride levels. (Berger et al., j. Biol. Chem., 1999, Vol 274, pp. 6718-6725). Later it has been shown that PPARδ activation leads to increased levels of HDL cholesterol in db/db mice (Leibowitz et al. FEBS letters 2000, 473, 333-336). Further, a PPARδ agonist when dosed to insulin-resistant middle-aged obese rhesus monkeys caused a dramitic dose-dependent rise in serum HDL cholesterol while lowering the levels of small dense LDL, fasting triglycerides and fasting insulin (Oliver et al. PNAS 2001, 98, 5306-5311). The same paper also showed that PPARδ activation increased the reverse cholesterol transporter ATP-binding cassette A1 and induced apolipoprotein A1-specific cholesterol efflux. The involvement of PPARδ in fatty acid oxidation in muscles was further substantiated in PPARα knockout mice. Muoio et al. (J. Biol. Chem. 2002, 277, 26089-26097) showed that the high levels of PPARδ in skeletal muscle can compensate for deficiency in PPARα. In addition to the effects on cholesterol homeostasis, PPARδ treatment was observed to lower plasma glucose and insulin and improve insulin sensitivity in diabetic ob/ob mice and high fat diet induced insulin resistant mice (PNAS 2003, 100, 15924-15929). Taken together these observations suggest that PPARδ activation is useful in the treatment and prevention of Type 2 diabetes and cardiovascular diseases and conditions including atherosclerosis, hypertriglyceridemia, and mixed dyslipidaemia (WO 01/00603).
A number of PPARδ compounds have been reported to be useful in the treatment of hyperglycemia, hyperlipidemia and hypercholesterolemia (WO 02/59098, WO 01/603, WO 01/25181, WO 02/14291, WO 01/79197, WO 99/4815, WO 97/28149, WO 98/27974, WO 97/28115, WO 97/27857, WO 97/28137, WO 97/27847 WO 2004093879, WO 2004092117, WO 2004080947, WO 2004080943, WO 2004073606, WO 2004063166, WO 2004063165, WO 2003072100, WO 2004060871, WO 2004005253, WO 2003097607, WO 2003035603, WO 2004000315, WO 2004000762, WO 2003074495, WO 2002070011, WO 2003084916, US 20040209936, WO 2003074050, WO 2003074051, WO 2003074052, JP 2003171275, WO 2003033493, WO 2003016291, WO 2002076957, WO 2002046154, WO 2002014291, WO 2001079197, WO 2003024395, WO 2002059098, WO 2002062774, WO 2002050048, WO 2002028434, WO 2001000603, WO 2001060807, WO 9728149, WO 2001034200, WO 9904815, WO 200125226, WO 2005097098, WO 2005097762, and WO 2005097763.
Glucose lowering as a single approach does not overcome the macrovascular complications associated with Type 2 diabetes and metabolic syndrome. Novel treatments of Type 2 diabetes and metabolic syndrome must therefore aim at lowering both the overt hypertriglyceridaemia associated with these syndromes as well as alleviation of hyperglycaemia. This indicate that research for compounds displaying various degree of PPARδ activation should lead to the discovery of efficacious triglyceride and/or cholesterol and/or glucose lowering drugs that have great potential in the treatment of diseases such as type 2 diabetes, dyslipidemia, syndrome X (including the metabolic syndrome, i.e. impaired glucose tolerance, insulin resistance, hypertrigyceridaemia and/or obesity), cardiovascular diseases (including atherosclerosis) and hypercholesteremia.